Radio transmitter



March 16, 1945. uss M 2,313,850

RADIO TRANSMITTER Filed Feb. 8, 1941 I Z M-v-f/l/ ATTORNEY Patented Mar. 16, 1943 RADIO TRANSMITTER George L. Usselman, Port Jefierson, N. Y., assignor to Radio Corporation of America, a corporation of Delaware Application February s, 1941, Serial No. 377,981

12 Claims.

This invention relates to a new and useful radio transmitter circuit.

An object of this invention is to provide a simple form of transmitter which is compact and inexpensive to manufacture.

Another object of this invention is to provide a transmitter for use. on armored tanks and trucks where the transmission is generally over very short distances and at fairly low frequencies.

Another object of this invention is to provide an improved transmitter circuit which will very effectively preventharmonic radiation, which is a very desirable feature,,where a large number of different transmitters are required to transmit within closeproximity to one another.

A feature of this invention is the novel arrangement of an oscillator which is coupled to an antenna by a crystal element which performs the dualfunction of ,controlling the transmitter frequency and coupling the antenna circuit to the oscillation circuit.

This invention will best be understood by referring to the accompanying drawing, in which:

Fig. 1 is a circuit diagram of this invention employing a three-element tube; and r I Fig. 2 is a circuit diagram of this invention employing a screen grid tuba 1 Referring now in detail to Fig. 1, there is shown an oscillation generator circuit including an electron discharge device [having a grid 2, plat 3 and cathode 4. An inductance 5 is connected to plate ,3. A key 6 is connected in series with inductance 5 and a source of B. voltage supply 1. A condenser 8, which may bein the orde'r'of .01 to. .1 mfdl," is connected from the lower side of inductance 5 to one side of the cathode 4. The

cathode 4 is heated by any suitable voltage source,

such as a battery, shown at ,9. A crystal! is coupled between plate 3 and grid 2 by means of metallic electrodes II and I2. A resistance l'3, having a value inthe order'of from 5,000 to 100,000 ohms,connects from grid 2 to the negative side of the B battery 1. An antenna I4 is coupled to crystal H] by means of condenser plates or electrodes I5 and Hi. The crystal frequency may be from 100 kc. to 5,000 kc. Although a dipole type of antenna is shown, it should not be limited thereto, as an ordinary antenna may function equally as well. A metallic shield I1 is interposed between electrodes l I and I5 and I2 and IS,

the shield being connected to ground at [8. If

desirable, the key 6 could be replaced by any suitable form' of microphone.

Referring now in detail to the circuit diagram ilar to that shown in Fig. 1, except that a screen grid tube 2A is shown connected to a microphone 6A. The shield [1A is shown as completely shielding the oscillation circuit. The by-pass condenser 8A which connects between the screen grid and cathode 4 may be in the order of .0005 to .001 mfd. The other values of component parts are generally similar to that shown in Fig. 1; the microphone 6A may be the variable conductance type, such as carbon granules. A magnetic or piezo-electric crystal or a condenser type of microphone may be used with a transformer in the screen grid circuit. The crystal electrodes l5 and It may be connected to the antenna through lines 19 and 20, as shown in the drawing.

The general principle of operation of a crystal oscillator using the crystal connected between the anode and the control grid is well knownand need not be explained. The invention resides in the idea of coupling the antenna to the crystal instead of the oscillator circuits, as it is usually done. This means that the antenna coupling to the transmitter is through the mechanical vibrations of the crystal. These vibrations cause oscillating electrical potentials to appear on the crystal electrodes which are in turn coupled to the antenna andthe transmitter. Those skilled in the art understand these phenomena. It should be pointed out that the crystal element not only is a coupling filter between the antenna and the transmitter oscillating circuit but it is animportant'part of the oscillating circuit, being the device which controls the transmitter frequency.

Although only two forms of this invention are shown, it is to be distinctly understood that it is not to be limited precisely thereto.

What is claimed is: e

l. A radio transmitter comprising an electron discharge device oscillation generator having at least anode, grid and cathode circuits, an antenna, a frequency determining circuit for said generator comprising a crystal element having at least four electrodes, one of said electrodes condischarge device oscillation generator having at shown in Fig. 2, the arrangement is generally simleast anode, grid and cathode circuits, an antenna, a frequency determining circuit for said generator comprising a crystal element having at least four electrodes, one of said electrodes connected to said anode circuit, and another electrode connected to said grid circuit, the two remaining electrodes being arranged to couple said oscillation generator to said antenna, and a metallic shield interposed between said oscillation generator and said antenna.

3. A radio transmitter comprising an electron discharge device oscillation generator having at least anode, grid and cathode circuits, an antenna, a frequency determining circuit for said generator comprising a crystal element having at least four electrodes, one of said electrodes connected to said anode circuit and another electrode connected to said grid circuit, the two remaining electrodes being arranged to couple said oscillation generator to said antenna, and means for modulating the oscillations produced by said oscillation circuit.

4. A radio transmitter comprising an electron discharge device oscillation generator having at least anode, grid and cathode circuits, an antenna, a frequency determining circuit for said generator comprising a crys'talelement having at least four electrodes, one of said electrodes connected to said anode circuit and another electrode connected to said grid circuit, the two remaining electrodes being arranged to couple said oscillation generator to said antenna, any keying means for modulating the oscillations produced by said oscillation circuit.

5.'A radio transmitter comprising an elec tron discharge device oscillation generator having at least anode, grid and cathode circuits, an antenna, a frequency determining circuit for said generator comprising a crystal element having at least four electrodes, one of said electrodes connected to said anode circuit and another electrode connected to said grid circuit, the two remaining electrodes being arranged to couple said oscillation generator to said antenna, and microphone means for modulating the oscillations produced by said oscillation circuit.

6. A crystal oscillator whose frequency of oscillations is determined primarily by the crystal, a pair of electrodes for said crystal and connections from said oscillator to said pair ofelectrodes, and another pair of electrodes for said crystal so disposed as to receive voltages generated only by the motion of said crystal, and means forderiving energy from said oscillator connected to said last pair of electrodes.

7. An oscillation generator system including a tubehaving a grid and an anode, a crystal for controlling the frequency of oscillations of said generator, said crystal having a first pair of cooperating electrodes and an independent pair of cooperating electrodes so arranged that coupling between said pairs of electrodes is obtained solely by virtue of the mechanical motion of the crystal, connections from the grid and anode to said first pair of cooperating electrodes, and

a load circuit connected to said independent pair of cooperating electrodes.

8. An oscillation generator system including a tube having grid and anode electrodes, a crystal having a pair of cooperating electrodes on two surfaces thereof and an independent pair of cooperating electrodes on two surfaces thereof, connections from said grid and anode to one pair of cooperating electrodes, and an antenna circuit connected to the other pair of cooperating electrodes, whereby the frequency of oscillations produced by said generator system is controlled by said crystal.

9. An oscillation generator system including a tube having grid and anode electrodes, nonresonant elements for supplying energizing potentials to the tube electrodes, a crystal having a pair of cooperating electrodes on two surfaces thereof and an independent pair of cooperating electrodes on two surfaces thereof, connections from said grid and anode to one pair of cooperating electrodes, and an antenna circuit connected tothe other pair of cooperating electrodes, whereby the frequency of oscillations produced by said generator system is controlled by said crystal.

10. An oscillation generator system including a tube having grid and anode electrodes, a crystal having a pair of cooperating electrodes on two surfaces thereof and an independent pair of cooperating electrodes on two surfaces thereof, connections from said grid and anode to one pair of cooperating electrodes, an antenna circuit connected to the other pair of coope'rat ing electrodes, whereby the frequency of oscillations produced by said generator system is controlled by said crystal, and means for modulating the oscillations produced by said gem erator.

11. An oscillation generator system including a tube having grid and anode electrodes, a crys= tal having a pair of cooperating electrodes on two surfaces thereof and an independent pair of cooperating electrodes on said-same two surfaces thereof, connections from said grid and anode to one pair of cooperating electrodes, an antenna circuit connected to" the other pair of cooperating electrodes, whereby the frequency of oscillations produced by said generator system is controlled by'said crystal, and a shield between said twopairsof cooperating electrodes, whereby the coupling betweensaid pairs of electrodes is obtained solely by virtue of the mechanical motion of the crystal.

. 12. A crystal controlled radio transmitter comprising an oscillation generator circuit, a crystal element for determining the frequency of said generator circuit, said crystal element including a pair of crystal electrodes, and an antenna coupled to said pair of crystal electrodes, whereby said crystal element performs the dual function'of controlling the transmitter frequency and coupling said antenna tdsaid oscillation generator circuit.

GEORGE L. 

